Five of the six senior GlaxoSmithKline executives cited by a whistleblower as part of a cover-up of contamination problems at the group's Puerto Rico factory are understood to still be employed by the pharmaceuticals company.

Cheryl Eckard, who was sacked by the company as a quality control manager in 2003 after repeatedly raising her concerns with a series of GSK executives, received a $96m (£61m) reward this week as part of a $750m criminal and civil settlement between US regulators and the company.

Her evidence stated that she believed company executives refused to acknowledge the gravity of the production violations – which included the wrong strength of pills being shipped – because it would delay the approval of two new drugs by the US Food and Drug Administration.

The court documents allege that Eckard, who had recommended the factory be shut until the issues were resolved, communicated the quality violations at the plant in Cidra to David Pulman, president of global manufacturing and supply; Janice Whitaker, senior vice president of global quality; Peter Savin, vice president of global quality assurance; Diane Sevigny, director of global quality assurance, risk management and compliance; and Jonathan Box, vice president of manufacturing and supply for North America.

All five executives are believed to be still working for the London-listed company, while Pulman is also a member of the company's 18-strong corporate executive team, which includes chief executive Andrew Witty.

The whistleblower's evidence states: "Eckard now believes that Whitaker, Pulman and other GSK executives were unwilling to acknowledge the gravity of the violations at the Cidra plant and to take the action that Eckard had recommended in part because the FDA had indicated that it would not consider approvals for [GSK drugs] Avandamet and Factive until [a previous FDA warning was] resolved."

It further outlines how "on or about April 2, 2003, Eckard delivered to GSK senior managers Box, Savin, Whitaker and Sevigny … a non-routine detailed memorandum on Current Compliance Risks for Manufacturing and Supply of Drug Products at Cidra … She did not receive any response to her memorandum from any of the managers."

Eckard also states that she told Sevigny "that she would not participate in a cover-up … and would not take part in any further meetings with the FDA about the Cidra plant … During this period and thereafter, Eckard and Sevigny were in frequent and increasing conflict about GSK's management of the quality and compliance problems at Cidra."

After 10 months of repeatedly alerting a string of GSK executives to the problems, Eckard was sacked in 2003. In July of that year, she telephoned JP Garnier, GSK's then chief executive, who declined to take the call. Eckard then reported the company to the FDA in August 2003.

A spokesman for GSK declined to discuss the five executives or confirm that they still worked for the company. She said: "I think it is also important to reiterate our commitment to patient safety and compliance with cGMP [current Good Manufacturing Practice], which has been demonstrated by the fact that we have not received an FDA warning letter at any plant since the Cidra facility was cited in July 2002."

The company has pleaded guilty to five breaches of quality standards, including those relating to certain lots of Kytril – an anti-nausea drug used for cancer patients – being released when "the manufacturing processes and laboratory testing were insufficient to assure the medicine was of the quality and purity required" and certain lots of diabetes treatment Avandamet being released before the company was sure the drug "was of the strength, identity, quality and purity required".

The company says that, aside from those five specific breaches, it "denies all other government allegations and the allegations by Ms Eckard".